1. Field of the Invention
The present invention relates to an encased photographic material and, more particularly, to an encased photographic material in which the storage stability of a silver halide photographic light-sensitive material encased in a light-transmitting case is improved.
2. Description of the Related Art
Silver halide photographic light-sensitive materials are sensitive to light. Therefore, such materials are generally shielded from light during storage before used in photographing. For example, the light-sensitive material is set in a lightproof container such as a magazine or cartridge, such as a film cartridge of 135-format color negative film. The cartridge containing the light-sensitive material is often encased in a light-transmitting or transparent case. The transparent case allows easy observation of the cartridge encased therein. Further, the transparent case can be conveniently reused as a case for keeping small articles.
Recently, a surprising phenomenon has been found: photographic film products placed on shelves in stores for long periods of time vary in film performance depending on brightness with which they are placed. An analysis of this phenomenon revealed that a certain kind of gas was generated by light incident on the leader portion of a film in a cartridge, through a paper box containing a transparent case encasing the cartridge and this gas diffused to a film portion shielded from light in the cartridge, changing the performance of the film. No such phenomenon has been conventionally known to those skilled in the art. To analyze this gas, a photographic film was forced to be irradiated with intense light and gas produced was collected. The gas was found to contain hydrogen cyanide gas.
Meanwhile, the present inventor has made extensive studies on an emulsion in which at least 60% of the total projected area of silver halide grains are occupied by tabular grains having an aspect ratio of 3 or more. A tabular grain has a large surface area and can therefore adsorb a large amount of sensitizing dyes. This increases a light absorption amount, resulting in an increased light sensitivity. In addition, a pressure-resistant property can be improved by introducing, on an average, 10 or more dislocation lines per grain. However, it is found that the presence of dislocation lines in tabular grains significantly increases the change in photographic performance due to irradiation with light. It is considered that this significant increase in change is due to the following two causes: the presence of dislocation lines in tabular grains increases an amount of halogen gas produced by print out; the presence of dislocation lines in tabular grains impairs the resistance of silver halide grains against hydrogen cyanide gas. These are serious problems in using tabular grains having dislocation lines. The deterioration caused by hydrogen cyanide gas is particularly significant when the grains are sensitized with gold and chalogen.